A simple web search can return results for in-ground pool schematics. Poolcenter.com is one of many websites that supply diagrams for plumbing in-ground pools and spas.
Although there are several different types of pools, filtering and circulation are imperative for keeping all varieties clean. Every pool usually has a drain at the lowest point of the floor and a skimmer. The drain suctions debris that falls to the bottom, while the skimmer suctions floating debris like leaves or bugs. The plumbing system then pumps the water being suctioned through the drain and skimmer through a large filter and back out to the pool.